A polyimide film has excellent thermal and mechanical properties. Recently, as the demand for high-temperature materials has increased, the necessity of use thereof has been on the rise. However, a polyimide film has been used restrictively because it is expensive.
Particularly, in the fields of displays, a polyimide film having excellent thermal and mechanical properties as well as excellent optical properties has attractive considerable attention lately.
Thus, as the requirement for an inexpensive polyimide film having excellent thermal, mechanical and optical properties increases, attempts to mix a polyamide with a polyimide (a main material of a polyimide film) or to copolymerize them are being made.
However, a polyamide-imide copolymer film satisfying optical properties as well as thermal and mechanical properties required in the market is not actually provided yet.